So the death of Kreia at the hands of the Exile would create echoes because with her death die the ideals of the old jedi order right? And she wants to continue the "tradition" of the Sith in which the apprentice kills the master once the former is stronger?

And why does Wookiepedia say that the final destruction of Malachor "sealed" the wound?

Kreia says the above line to the Exile on the Ebon Hawk. She wasn't lying this time and at Malachor, the two of them were not caught unaware, thus Kreia's death DID NOT lead to the Exile's death.

Another thing, when Moza the Ithorian visits us on Telos for the first time in Residential Module 082 he says that upon the Exile's arrival, Chodo Habat felt a "disturbance or echo in the force"

So does even a simple thing like the Exile's arrival on Telos create echoes in the Force? Just because of what the Exile went through at Malachor V, his arrival on planets can be sensed by other Force sensitives?

Well that is nothing new, we knew of that in the first Star Wars movie where Vader senses Obi-Wan on board the Death Star